one week of boxercise to training 4-5 nights a week. am i overdoing it?
eh yes. you need to gradually increase training load not rip straight into sessions every night. gradually. it doesnt matter what trainers you're wearing, if you're doing far more than your muscles are able for you're going to be sore.
there are a lot of decent running sites around that give detailed training plans for working towards different distance runs. take a look an see.